With the term "elastosols" as used throughout this specification is meant dispersions of very fine elastomeric block copolymer particles in liquid organic media, or more specifically, in rubber compatible liquid plasticizers.
At present polyvinylchloride plastisols, i.e. dispersions of very fine PVC particles in liquid organic media, are widely used for a variety of applications, such as in the preparation of bottle cap seals, conveyor belts, carpet backing, wall-coverings, and floor-coverings. In other applications PVC plastisols are processed by means of dipping, such as in the case of industrial gloves, surgical gloves, shoes, boots and coated wire products. The shaping of products by means of roto-casting or molding, which is the reverse of dipping, is also a widely used technique. The latter method is particularly suited for the production of hollow goods, such as certain toys (balls, dolls and the like).
Since there is an increasing demand for environmental friendly products, PVC containing compositions are the subject of many discussions due to the presence of the environmentally charging element chlorine in PVC. It will be appreciated that upon disposal of PVC containing products, e.g. by incineration, toxic compounds containing chlorine may be released into the environment. Therefore, extensive research effort is put in by industry to find halogen-free alternatives for PVC. However, a significant problem is to find such alternatives which provide at least the same processing and product characteristics as the presently applied PVC plastisols.
One of the main advantages of using PVC plastisols namely, is their ability to be processed by the above mentioned inexpensive processing techniques, such as spreading, molding or roto-casting and dipping, followed by zero-shear fusion of the plastisol to form the desired product. These techniques are much more flexible and provide higher production speeds than the conventional thermoplastics processing techniques like extrusion and injection molding. Up to now not any satisfactory halogen-free alternative for PVC plastisols has been found which can be prepared and processed according to said advantageous plastisol processing techniques. Moreover, as in the present situation these techniques are widely used in the PVC-plastisol industry, it is by far preferred to develop halogen-free alternatives which can be processed (and prepared) using the existing equipment in order to keep the investment costs as low as possible.
It will be appreciated that it is a main object of the present invention to provide a halogen-free PVC alternative in the form of a dispersion and more particularly in the form of an elastosol, which can be processed by means of the presently applied plastisol techniques.
From Canadian Patent No. 1,132,283 a composition is known containing a highly oil extended conjugated diene/vinyl aromatic radial teleblock copolymer. Said composition is prepared by dissolving the block copolymer in the oil under shear conditions, e.g. by stirring, and at an elevated temperature of 120.degree. C. to 205.degree. C. The radial block copolymer contains 50-95% by weight of the conjugated diene and 5-50% by weight of the monovinyl aromatic compound. Due to the relatively higher content of conjugated diene in comparison with the monovinyl aromatic compound, the radial block copolymer is highly elastic. The oil to be used preferably is a naphtenic oil as the bleeding-out of oil is most likely to occur if paraffinic oil is used. The weight ratio of polymer to oil may vary from 0.5 to 0.1, which implies that oil is always present in larger amounts than the polymer. As a result, the composition is rather soft and the complete absence of bleeding-out of oil is difficult to realize. Moreover, during the preparation of the composition, the radial teleblock copolymer must be dissolved at an elevated temperature in order to obtain a homogeneous blend eventually. The processing of such compositions prepared by this melt technique is rather difficult, as shaped articles or homogeneous films can only be prepared starting from a hot mixture. It will be appreciated that storage of the homogeneous blend is in fact impossible as homogeneity is only reached at elevated temperatures and after cooling the resulting product is too stiff to be processed any further. So after its preparation, the homogeneous blend immediately must be processed.
Hence, it would be advantageous to provide an elastosol, which is stable at room temperature and which consequently can be prepared, handled and stored at relatively low temperatures. Heating the elastosol is carried out only after the elastosol has been brought in its desired end shape.
It is therefore another object of the present invention to provide a process for the preparation of an elastosol, which process can be carried out at relatively low temperature, in order to obtain an elastosol which is stable at room temperature.
A further object of the present invention is to provide a process for the preparation of a product obtainable from said elastosol via a phase inversion process.